In conventional sets of iron golf clubs, each club includes a shaft with a club head attached to one end and a grip attached to the other end. The club head includes a face for striking a golf ball. The angle between the face and a vertical plane is called the loft. In general, the greater the loft of the golf club is in a set, the greater the launch angle and the less distance the golf ball will travel when hit.
A set of irons generally includes individual irons that are designated as number 3 through number 9, and a pitching wedge. The iron set is generally complimented by a series of wedges, such as a lob wedge, a gap wedge, and/or a sand wedge. Sets can also include a 1 iron and a 2 iron, but these clubs are generally sold separately from the set. Each iron has a shaft length that usually decreases through the set as the loft for each club head increases, from the long irons to the short irons. The length of the club, along with the club head loft and center of gravity impart various performance characteristics to the ball's launch conditions upon impact. The initial trajectory of the ball generally extends between the impact point and the apex or peak of the trajectory. In general, the ball's trajectory for long irons, like the 3 iron, is a more penetrating, lower trajectory due to the lower launch angle and the increased ball speed off of the club. Short irons, like the 8 iron or pitching wedge, produce a trajectory that is substantially steeper and less penetrating than the trajectory of balls struck by long irons. The mid irons, such as the 5 iron, produce an initial trajectory that is between those exhibited by balls hit with the long and short irons.
Iron club heads are categorized into several different types: including muscle back, cavity back and hollow irons. In general, muscle back irons have an evenly distributed weight through the length of the iron from heel to toe. Thus, they have a very solid feel, but low Moment of Inertia, MOI, about the vertical axis extending through the face center. Cavity back irons generally have a thinner section in the center of the back of the club and more mass around the perimeter, thus they are cavity back. The cavity back irons, in general, have a greater MOI about the vertical axis extending through the face center. Finally, hollow irons generally have thinner faces and have mass that is located further back from the face and on the perimeter, creating an even larger MOI than cavity back irons.